Viscous two-speed clutch

Abstract

Some embodiments of a clutch system may drive an output portion to rotate at a first rotational speed when the clutch surfaces are engaged and to rotate at a second rotational speed when the clutch surfaces are shifted to a disengaged position. The viscous two-speed clutch system may employ a viscous drive system that causes the output portion to rotate even when the clutch surfaces are disengaged. In such circumstances, the cooling fan can be driven to rotate at a first rotation speed due to interconnection with a drive source and to rotate at a second rotational speed even when the clutch surfaces are disengaged. Thus, the clutch system facilitates the flow of cooling air both when the vehicle cooling system activates the fan (e.g. by causing the clutch surface to engage) and when the vehicle cooling system deactivates the fan (e.g. by causing the clutch surfaces to disengage).

The invention claimed is: 
     
       1. A fan clutch device, comprising:
 an input member which is attached to a drive pulley so that the input member rotates with the drive pulley; 
 an enclosure attached to the input member so that the enclosure rotates with the drive pulley; 
 a piston which is movable between a first position and a second position; 
 a clutch ring with an engagement surface provided on an outer circumference of the clutch ring which selectively engages an opposing surface of the input member provided on an inner circumference of the input member; 
 a fan hub coupled to the clutch ring; 
 a spring provided between the clutch ring and the fan hub; 
 a fan member coupled to the fan hub; and 
 a shearing fluid provided in an axial space between the enclosure and the clutch ring, 
 wherein, when the piston is in the first position, the engagement surface of the clutch ring engages the opposing surface of the input member such that the clutch ring rotates at a first rotational speed substantially equal to a rotational speed of the drive pulley, 
 wherein, when the piston is in the second position, the engagement surface of the clutch ring disengages the opposing surface of the input member, and a shearing force, provided by the shearing fluid due to rotation of the enclosure, rotates the clutch ring at a second rotational speed less than the first rotational speed, and 
 wherein the axial space between enclosure and the clutch ring is disposed radially outward of the spring, and attachment fasteners which couple the clutch ring and the fan hub are disposed radially inward of the spring. 
 
     
     
       2. The fan clutch device according to  claim 1 , wherein the engagement surface of the clutch ring and the opposing surface of the input member are frustoconical. 
     
     
       3. The fan clutch device according to  claim 1 , wherein the enclosure and the clutch ring include matable non-planar surfaces. 
     
     
       4. The fan clutch device according to  claim 1 , further comprising a clutch shaft to which the piston is coupled. 
     
     
       5. The fan clutch device according to  claim 4 , further comprising a gear coupled to the clutch shaft and coupled to the input member. 
     
     
       6. The fan clutch device according to  claim 4 , further comprising a fluid-receiving chamber defined by the piston, the clutch shaft, and interior surfaces of the drive pulley. 
     
     
       7. The fan clutch device according to  claim 1 , wherein the spring is disposed in a cavity of the clutch ring. 
     
     
       8. A method for operating a fan clutch device, comprising:
 operating the fan clutch at a first rotational speed when a first operating condition is satisfied; and 
 operating the fan clutch at a second rotational speed less than the first rotational speed when a second operating condition is satisfied, 
 wherein the fan clutch comprises:
 an input member which is attached to a drive pulley so that the input member rotates with the drive pulley; 
 an enclosure attached to the input member so that the enclosure rotates with the drive pulley; 
 a piston which is movable between a first position and a second position; 
 a clutch ring with an engagement surface provided on an outer circumference of the clutch ring which selectively engages an opposing surface of the input member provided on an inner circumference of the input member; 
 a fan hub coupled to the clutch ring; 
 a spring provided between the clutch ring and the fan hub; 
 a fan member coupled to the fan hub; and 
 a shearing fluid provided in an axial space between the enclosure and the clutch ring, 
 wherein, when the piston is in the first position, the engagement surface of the clutch ring engages the opposing surface of the input member such that the clutch ring rotates at the first rotational speed substantially equal to a rotational speed of the drive pulley, 
 
 wherein, when the piston is in the second position, the engagement surface of the clutch ring disengages the opposing surface of the input member, and a shearing force, provided by the shearing fluid due to rotation of the enclosure, rotates the clutch ring at the second rotational speed, and 
 wherein the axial space between enclosure and the clutch ring is disposed radially outward of the spring, and attachment fasteners which couple the clutch ring and the fan hub are disposed radially inward of the spring. 
 
     
     
       9. The fan clutch device according to  claim 1 , wherein the enclosure includes:
 an outer radial portion including attachment holes substantially aligned with attachment holes of the input member, 
 an inner radial portion surrounding a bearing, and 
 an intermediate portion between the outer radial portion and the inner radial portion, and 
 wherein the enclosure is in front of the clutch ring in an axial direction such that a rear axial surface of the intermediate portion cooperates with a front axial surface of the clutch ring to provide the axial space for the shearing fluid.